My most recent project uses this wonderful 8 pin PIC that does nearly anything. If you havent looked at this device, then spend some time and check it out.

This project essentially is a bright red/blue LED lamp that turns on for 4 hours at dusk, then delays 14 hours, then looks again for night again. It is a 3 state Finite State Machine that uses a phototransistor to detect the room brightness, and detect either day or night. So far, it works great, and I hope this inspires you not only to try some sort of day/night photocell project yourself, but to consider the possibilities of this awesome PIC.